The present invention is directed to threat detecting and tracking radars, in general, and more particularly, to a system of the radar which adaptively assesses a detected threat in accordance with derived relative bearing representative measurements thereof to determine the collision potential of the threat with the radar.
Many modern airborne radars include a system to detect potential threats, like a seeking missile, for example. To avoid collision with the detected threat, these airborne radar systems alert the pilot when the potential threat comes within a given proximity range of the aircraft such that sufficient time is allowed for the pilot to dispense some type of counter measure. In general, these radar systems are designed in accordance with a failsafe philosophy which allows for false alarms, but does not permit a potential threat to go undetected. That is, all detected targets are considered as real threats unless they can be discriminated otherwise with a definite degree of certainty. Needless to say, a strict failsafe criteria with regard to threat detection causes a large number of false assessments which correspondingly result in an equal number of false dispensing of the countermeasure media. Since each countermeasure dispense is in itself a very expensive reaction, it becomes apparent that large numbers of false identification produce very high life cycle costs in operating these radar systems.
To reduce the number of false assessments, some radar systems rely upon special techniques to assess the various threat potentials in order to discriminate between false and real threats. The majority of tests are designed to discriminate between aircraft and seeking missiles and generally rely upon target radar signature and range-velocity characteristics as well as range proximity. One known discrimination technique utilizes an accurate radar cross-section derivation of the potential threat for an assessment. This test remains viable as long as the radar reflections from the potential threat fall within the main beam of the radar. However, because of the gain characteristics of the radar beam, when the radar reflections are received elsewhere, like on the edges of the radar beam, for example, the received signals may be attenuated as a result of the gain characteristics of the beam, thus reducing the apparent cross-sectional size of the target being assessed, making an aircraft target, for example, appear more in the shape of a missile or the like. Consequently, the potential threat may be assessed as a real threat causing a false countermeasure dispense to be activated needlessly.
Some radar systems employ additional tests to assist in the discrimination process to further clarify target identification. One of these tests relies on the drag characteristics of the missile in its collision course with the aircraft, that is, a missile tends to decelerate upon approaching the aircraft. Therefore, the combination of cross-section and deceleration calculation values of the potential threat is expected to provide a more accurate discrimination of the false threat and, indeed, this appears to be the case in many instances. However, there still remains certain flight conditions of the potential threat under which this combination of tests may not discriminate against aircraft false targets.
In this regard, suppose that a potential threat, which is an aircraft, for example, is detected along the side of the main beam of the radar antenna at a time when the aircraft is deviating from a collision course with the homecraft. As the aircraft deviates, it may decelerate. In this scenario, the radar computes an apparent cross-sectional signature of a missile which is decelerating, the combination rendering a positive indentification of a real threat even though in reality an aircraft avoiding collision is actually present.
For the most part, target cross-section radar signature, range-velocity characteristics and proximity tests in combination offer a viable and fairly accurate discrimination of aircraft targets from missile targets under fail-safe requirements. However, there are certain conditions or combinations of conditions under which the threat discrimination breaks down, resulting in a false dispensing of countermeasure media unnecessarily. To reduce further the life cycle operational costs of these threat detection radars, the present invention provides for a system offering still another discrimination test which may be used individually or in combination with the others to reduce the number of false identifications and thus reduce the life cycle cost of operating the radar system making it more economically attrative.